Protocols utilized among devices when a terminal device makes communication through a base station and a network can be divided into layers, as shown in FIG. 1. Examples of a layer model include a transmission control protocol (TCP)/internet protocol (IP) layer model, and an open systems interconnection (OSI) reference model formulated by the International Organization for Standardization. FIG. 1 represents, as an example of the layer model, the layers based on the TCP/IP layer model.
The TCP/IP layer model includes an application layer, a transport layer, an internet layer, and a network interface layer, from the top. In the application layer, superordinate to the transport layer, applications that utilize the protocol of the transport layer are located.
The application layer corresponds to an application layer, a presentation layer, and a session layer based on the OSI reference model. In addition, the internet layer corresponds to a network layer based on the OSI reference model.
Among the mentioned layers, a packet data convergence protocol (PDCP) controls transmission of communication data between the terminal device and the base station. In addition, a general packet radio service tunneling protocol for user plane (GTP-U) controls the transmission of communication data between the base station and a gateway device.
Examples of the protocol of the transport layer include the TCP and a user datagram protocol (UDP). Examples of the protocol of the internet layer include the IP. The IP controls the transmission of communication data between the terminal device and a server device, utilizing the PDCP and the GTP-U.
The TCP controls the transmission of the communication data between the terminal device and the server device, utilizing the IP. Accordingly, the terminal points of communication data in the transport layer and the internet layer are the terminal device and the gateway device or the server device, respectively.
Here, the processing performed by the TCP in the transport layer will be described. The TCP is a protocol to transmit communication data with a header added to the leading end thereof. The fields constituting the header include a window size, which is a parameter used for notifying a data amount that the receiving side can receive at a time, to the transmitting side. In other words, the window size corresponds to the size of the communication data that the transmitting side can transmit at a time, without the need to confirm the reception. The communication data based on the window size is transmitted, between the terminal device and the server device.
Regarding the control of the window size, for example, JP 2004-193841A, and JP 2016-174287A disclose that the gateway device or the server device configures the window size, based on a buffer capacity or contents to be distributed to the terminal device.
[PTL 1] JP2004-193841A
[PLT 2] JP2016-174287A
The wireless base station allocates a wireless resource to the terminal device, based on the situation of the wireless communication. Here, the amount of the wireless resource, allocated by the wireless base station to the terminal device, may differ from the window size of the data to be transmitted, for example, from the server device to the terminal device. In this case, the data amount transmitted and received between the terminal device and the server device may vary before and after passing through the wireless base station, which may provoke a congestion.